Miliary Tuberculosis
On this page
Direct answer
Miliary tuberculosis is haematogenous spread of Mycobacterium tuberculosis that forms innumerable small granulomas, usually 1 to 3 mm across, throughout the body. The chest radiograph shows a diffuse millet-seed pattern, and choroid tubercles on fundoscopy support the diagnosis. The tuberculin test is often negative because the immune response is overwhelmed. Treatment is standard anti-tubercular therapy, usually for six months, with a longer course for meningeal disease.
What you must remember
- Mechanism: blood-borne spread from a primary or reactivated focus, seeding the lungs, liver, spleen, bone marrow and other organs.
- Chest radiograph: diffuse, uniform 1 to 3 mm nodules throughout both lungs, giving the millet-seed appearance.
- Fundoscopy: small, pale, yellow-grey choroid tubercles are a useful clue when present.
- Laboratory clues: anaemia, raised alkaline phosphatase and hyponatraemia are common, and hepatosplenomegaly may be present.
- Tuberculin test: often negative in widespread disease, so it cannot exclude miliary tuberculosis.
- Treatment: the National Tuberculosis Elimination Programme standard regimen, usually six months, with a longer course for tuberculous meningitis and corticosteroids for meningeal or pericardial involvement.
A febrile patient who has lost weight
A 45-year-old man from an endemic area has three months of fever, night sweats, weight loss and a dry cough. His haemoglobin is low, his liver and spleen are palpable, and his chest film shows diffuse fine nodules.
Miliary tuberculosis should be suspected when prolonged fever, weight loss and hepatosplenomegaly occur together, especially with a diffuse chest pattern. Confirmation rests on samples from several sites.
- Recognise the picture: Prolonged fever, weight loss, night sweats, anaemia and organomegaly raise suspicion in an endemic setting.
- Image the chest: The chest film is reviewed, and high-resolution CT shows the nodules more clearly when the film is unclear.
- Examine the eyes: Fundoscopy is performed to look for choroid tubercles, which support the diagnosis.
- Send microbiology: Sputum or gastric aspirate, urine and bone marrow are sent for acid-fast smear, culture and molecular testing, since yield from several sites improves diagnosis.
- Biopsy if needed: Liver or bone marrow biopsy showing caseating granulomas supports the diagnosis when smears are negative.
- Start treatment early: Anti-tubercular therapy is started on strong clinical suspicion, and corticosteroids are added if meningeal disease is present.
Where the exam catches the cryptic form
The exam tests whether you avoid the traps that hide miliary disease.
- Trap: ruling out miliary tuberculosis because the chest film looks normal Correct: cryptic miliary disease can have an unremarkable film, especially in elderly or immunosuppressed patients.
- Trap: using a negative tuberculin test to exclude tuberculosis Correct: disseminated disease can suppress the test, so a negative result does not rule it out.
- Trap: treating tuberculous meningitis with the six-month regimen alone Correct: meningeal disease needs a longer course, typically around a year, with adjunctive corticosteroids.
- Trap: expecting the classic millet-seed pattern in every case Correct: cryptic forms show little or no nodularity, so biopsy and cultures are needed.
Frequently asked questions
What is the typical chest X-ray of miliary tuberculosis?
Miliary tuberculosis shows diffuse, uniformly distributed 1 to 3 mm nodules throughout both lungs, giving a millet-seed appearance. The film can be atypical in elderly or immunosuppressed patients, so CT is used when the chest X-ray is unclear.
Why is the tuberculin skin test often negative in miliary tuberculosis?
The tuberculin skin test is often negative in miliary tuberculosis because widespread disease suppresses the delayed hypersensitivity response, a state called anergy. A negative test therefore cannot exclude miliary tuberculosis in a patient with compatible features.
What is cryptic miliary tuberculosis?
Cryptic miliary tuberculosis is disseminated disease without the classic millet-seed chest pattern, more often seen in elderly, immunosuppressed or HIV-infected patients. It presents as fever of unknown origin with weight loss, and diagnosis depends on biopsy of the liver or bone marrow and cultures.
How long is treatment for miliary tuberculosis?
Miliary tuberculosis is treated with the standard intensive phase of four drugs followed by a continuation phase, usually giving six months in total. Tuberculous meningitis or other central nervous system involvement needs a longer course, typically around a year, with adjunctive corticosteroids.